Backlight gets reseted with VDPAU
I have an issue with the brightness of my laptop (VAIO VPCCW1S1E with GT230M) and I want to track down the cause of it. I have installed nvidiabl and it works great. The problem is that If I don't use composite of the window manager, then when I try to play a video with VDPAU output then the backlight is reseted to its' maximum value. If I use a composition window manager with opengl rendering, then the backlight is reseted even when I run a 3D app f.e. glxgears. If I use Xrender instead of opengl, then the backlight is not reseted neither with VDPAU nor with 3D apps. This happens in GNOME and KDE and it doesn't happen in another laptop with Intel integrated graphics. Do you have an idea of what might causing this behavior?